1. Field of the Invention
The present invention relates to a film formation method and a film formation apparatus which form a thin film containing an impurity on a surface of an object to be processed such as a semiconductor wafer or the like.
2. Description of the Related Art
In general, various processes, such as film formation, etching, oxidation, diffusion, surface modification, native oxide removal, or the like, are performed on a semiconductor wafer including a silicon substrate or the like in order to manufacture a semiconductor integrated circuit. From among the various processes, film formation will be exemplarily explained. During manufacture of a semiconductor integrated circuit, for example, a DRAM or the like, film formation process may be performed by forming recess portions, such as contact holes, through-holes, wiring grooves, cylindrical grooves of a capacitor having a cylindrical structure, or the like, in an insulating film formed on a surface of a semiconductor wafer and filling the recess portions with a conductive thin film.
A silicon film containing an impurity has been conventionally used as the thin film filled in the recess portions, because the silicon film has a relatively good step coverage and a relatively low cost. A method of filling the recess portions will be explained with reference to FIGS. 12A and 12B. FIGS. 12A and 12B are views showing an example where recess portions formed on a surface of a semiconductor wafer are filled.
As shown in FIG. 12A, an insulating film 2 formed of, for example, SiO2 or the like, is thinly formed on a surface of a semiconductor wafer W including, for example, a silicon substrate or the like, which is an object to be processed, and recess portions 4 are formed in the insulating film 2. The recess portions 4 are contact holes for contact with a lower layer or the substrate itself, through-holes, wiring grooves, cylindrical grooves of a capacitor having a cylindrical structure, or the like. Contact holes for contact with the substrate itself are exemplarily shown in FIG. 12A. And, as shown in FIG. 12B, a conductive thin film 6 is formed on the surface of the semiconductor wafer W in order to fill the recess portions 4. A silicon film containing an impurity is often used as the thin film 6 as described above.
As a film formation method of forming the thin film 6, a film formation method (Patent Reference 1) of forming a single crystalline thin film including an impurity at a low pressure of about 1 to 10−6 Pa by alternately supplying a gas including an element of silicon that is a semiconductor, for example, SiCl4 or the like, and a gas including an impurity element, such as BCl3 or the like, a film formation method (Patent Reference 2) of alternately forming a polysilicon layer by supplying, for example, a monosilane (SiH4) gas, and a phosphorus adsorptive layer by supplying a phosphine gas, a film formation method (Patent Reference 3) of forming a film by CVD (Chemical Vapor Deposition) by simultaneously supplying monosilane and boron trichloride (BCl3), and so on are known.
3. Prior Art Reference    (Patent Reference 1) Japanese Patent Laid-Open Publication No. sho 61-034928    (Patent Reference 2) Japanese Patent Laid-Open Publication No. hei 05-251357    (Patent Reference 3) Japanese Patent Laid-Open Publication No. hei 08-153688